Multi-pollutant crisis in Delhi-NCR: Ozone pollution another deadly contributor

With high pollution levels and growing heat stress due to climate change, the ozone level is frequently exceeding the standards

By Shambhavi Shukla
Published: Monday 05 June 2017

What do the findings suggest?

Early deaths due to ozone pollution are the highest in India. Credit: Robert_z_Ziemi / PixabayOn the eve of the World Environment Day, the Centre for Science and Environment (CSE) has a word of caution: no one is safe from deadly ozone pollution. According to an analysis done by the CSE, Delhi has witnessed significant ozone build-up this summer, adding to public health risk. CSE has analysed real-time air quality data available from key monitoring locations of the Delhi Pollution Control Committee for the summer months of 2016 and 2017.

The analysis shows ozone pollution in the city is worsening progressively with the onset of summer. With high pollution levels and growing heat stress due to climate change, the ozone level is frequently exceeding the standards and rising to poor and very poor levels—as classified by the National Air Quality Index (NAQI). In addition, heat waves and sunshine have increased the frequency of days with unhealthy levels of ozone. Ground-level ozone is not directly emitted by any source. This is formed when oxides of nitrogen (NOX) and a range of volatile gases, primarily from vehicles and other sources, are exposed to each other in sunlight.

According to Anumita Roychowdhury, executive director, research and advocacy and head of CSE’s air pollution programme: “Delhi and the National Capital Region (NCR) are in the grip of multi-pollutant crisis. Even before the health risk from particulate matter could be addressed, deadly ozone has raised its ugly head in Delhi and NCR. Without a time-bound implementation strategy and preventive action, this can deepen into serious public health crisis. This will spare neither the rich nor the poor.”

The ozone data was analysed from February to May from four stations: R K Puram, Punjabi Bagh, Mandir Marg and Anand Vihar to understand ozone build-up during summer.

Ozone spikes as summer progresses: This year, as summer progressed from February to May, the ozone built up rapidly and the number of days exceeding the ozone standard increased. The share of days violating the 8-hour CPCB standard of 100 microgramme per cubic metre (µg/m³) in February was 12 per cent, which increased to 19 per cent in March, 52 per cent in April and finally a whopping 77 per cent in May.

The level of ozone has doubled up quickly as the heat wave hit Delhi in May and the peak was three times higher than the standard. This is of serious concern as even short-term exposure to high ozone levels can cause great harm. This is one of the reasons why ozone standards are set for eight-hour average as well as one-hour average.

Days violating the ozone standard are higher this year: The number of days in April and May 2017 violating the eight-hour standard is higher this year compared to the previous year. In 2017 summer, as much as 64 per cent of days during April and May violated the standard as opposed to 50 per cent of days during April and May in 2016.

More days in ‘very poor’ category this year: Not only have the total number of days that have violated the standards increased this year, the severity of the problem has also grown. In 2017 summer (April-May), 8 per cent of days are in ‘very poor’ category as opposed to 4 per cent during the same months in 2016. However, the summer of 2016 had higher number of days in the ‘poor’ category.

Heat wave and high solar radiation with increased ambient temperature during summer is making the problem worse. The CSE has analysed the relationship between ozone build-up on one hand and increased solar radiation and rising ambient temperature on the other. Due to higher temperature and solar radiation, ozone concentration has also increased. For example, in April 2017, as the temperature increased from 27°C on April 9 to 32°C on April 14, the daytime ozone levels increased by 134 per cent or 2.34 times—rising from 90 to 211 µg/m³.

A similar trend is observed in May. When temperature rose from 32°C on May 3 to 36°C on May 8, the daytime ozone concentration increased by 130 per cent or 2.3 times from100 µg/m³ to 230µg/m³. This is ominous. With climate change and higher frequency of extreme weather events, such trends will put citizens at serious public health risk. 

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